An example of where an apparatus for lubricating pipe joints is used is in the field of earth drilling, especially for the petroleum industry. During earth drilling operations drilling fluids, commonly referred to as "drilling mud", are pumped down an annulus of a plurality of joined sections of drill pipe forming a drill string. Since the drilling mud is pumped at high pressure, each joint in the drill string must be perfectly sealed to prevent leakage. Leakage results in a washing action that can severely weaken the joint and cause it to fail. If the joint should fail, all that portion of the drill string below the failed joint is dropped down the borehole, and must be fished out at great expense.
Each joint has a male to female form of threaded connection. In order to prevent the joints from leaking they are screwed together under high torque. Two pieces of steel under pressure will not slide without tearing at each other and causing what is termed as "galling". Lubricating compounds form a thin gasket between the two pieces of steel forming the joint, which has a much lower sheer strength than steel. When the joint is made up the presence of the lubricating compound prevents metal to metal contact. When the joint is disassembled the lubricating compound is sheered, rather than the steel.
An apparatus for lubricating pipe joints which is presently in use has a generally cylindrical plug adapted to fit into a female box connection of a length of drill pipe. The plug has an exterior surface and a blind interior bore. A plurality of lubrication passages extend from the blind interior bore to the exterior surface of the plug. The exterior surface has a network of channels communicating with the lubrication passages. In operation, lubrication compounds are pumped under pressure into the blind interior bore. The lubrication compounds pass from the blind interior bore, through the lubrication passages and along the network of channels to thoroughly coat the exterior surface of the plug and, hence, the female box connection with lubricant.
The most important part of each connection is the mating shoulders. A weakness in apparatus used for lubricating pipe joints is that they cannot lubricate this critical portion of the joint. Of necessity the shoulders have been lubricated manually. This procedure is time consuming. Frequently, insufficient care is taken in the manual lubrication procedure and the lubrication proves to be inadequate.